Increase of Rostral Teeth with Development of a Freshwater Shrimp, Paratya compressa improvisa in the Tsurugata Marsh, Akita Prefecture

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Other Title
  • 秋田県鶴潟沼に生息するヌカエビの成長に伴う額角歯の増加
  • アキタケンツルガタヌマ ニ セイソク スル ヌカエビ ノ セイチョウ ニ トモナウ ガクカクシ ノ ゾウカ

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Abstract

The shrimp, Paratya compressa, is widely distributed in freshwater throughout Japan, except Hokkaido. The species is divided into two subspecies, P. c. compressa and P. c. improvisa by the presence or absence of the rostral teeth on the carapace. The rostral teeth of the former subspecies increase in number during the early stages of its life and the number of teeth at the adult stage plays a significant role in the identification of the two geographical groups. Thus it is important to determine the size of shrimp at which number of the rostral teeth is completed. The present study is based on the specimens of P. c. improvisa collected in the Tsurugata Marsh, Akita Prefecture. Ovigerous females had an average of 10.5 rostral teeth on the upper side and 2.4 rostral teeth on the lower side. The initial rostral tooth on the upper side appeared at the sixth zoeal stage, while the one on the lower side appeared at the eighth stage. The mean number of rostral teeth increases with development of the shrimp, and attains 10.0 on the upper side or 2.3 on the lower side, when the shrimp grow to 12 mm in body length, the size where the animals can be first segregated by sex. Sexual dimorphism was not found significant in the number of the teeth. After having grown to 13 mm, the shrimp had 2.4 teeth on the lower side, the average which was the same as that of the ovigerous female. On the other hand, the mean number of teeth on the upper side was 10.5 in 15 mm or larger shrimp. These results indicate that studies of geographical variation or other studies based on the number of rostral teeth need to use only individuals larger than 15 mm in body length.

Journal

  • Aquaculture Science

    Aquaculture Science 52 (3), 259-264, 2004

    Japanese Society for Aquaculture Science

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